Materials for electronic and electrical equipments require properties such as electrical conductivity, strength, and bending workability, and a demand for materials that allow high current is increasing in recent years for electric and electronic parts, particularly for movable connectors. In order to avoid movable connectors such as floating type connectors becoming larger, a material having good bendability as well as securing high electrical conductivity and strength, even at a thickness of 0.2 mm or more, is necessary.
Conventionally, Cu—Ni—Si, Cu—Co—Si, or Cu—Ni—Co—Si copper alloys are known as precipitation strengthened copper alloys having properties that allow for achieving high strength without deteriorating electrical conductivity. In order to manufacture these copper alloys, supplemented element(s) are solutionized by solution treatment, followed by cold rolling and aging treatment to precipitate or crystallize Ni2Si and Co2Si etc. as second phase particles in the matrix. However, since the amount of solubility of Ni2Si is relatively large, it is difficult to achieve an electrical conductivity of 60% IACS or more with a Cu—Ni—Si copper alloy. For this reason, Cu—Co—Si or Cu—Ni—Co—Si alloys containing Co2Si with low amount of solubility as the main precipitate and showing high electrical conductivity are being researched. The target strength cannot be achieved with these copper alloys unless they are sufficiently solutionized first and then precipitated to form fine precipitates. However, because solution treatment at a high temperature will cause coarsening of crystal grains resulting in problems such as deteriorated bending workability, various countermeasures have been investigated.
In Japanese Published Unexamined Patent Application Nos. 2009-242814 (Patent Document 1) and 2008-266787 (Patent Document 2), in order to manufacture a precipitation strengthened copper alloy for materials for electric and electronic parts such as a lead frame, the effect of suppressing crystal grain growth by second phase particles is utilized to control grain size and to improve bending workability. In the above documents, second phase particles precipitate during the cooling process in hot working or the temperature elevation process in solution heat treatment, as well as during the aging treatment after grinding ([0025] in Patent Document 1 etc.) In addition, International Publication No. 2009/096546 (Patent Document 3) describes a method in which the limitation of grain size and the fine size of precipitates are controlled in a Cu—Co—Si alloy having a specific composition, specifically, a method of controlling grain size by solution treatment temperature, cooling rate after solution treatment, and aging treatment temperature.
Patent Document 1
Japanese Published Unexamined Patent Application No. 2009-242814A
Patent Document 2
Japanese Published Unexamined Patent Application No. 2008-266787A
Patent Document 3 WO2009/096546